[WhatReef]

i highly doubt he damaged anything i have a lion fish as wel if you let the water get to bad they will start to form a slim over there body i dunno if this is your case but do his eyes appear to be glazed over if so this is from bad water conditions , the lion fish have a mucas that surrounds there bodys and keeps parasite off them and if they get a parasite or disease they usually will shed the mucas off there body, the best treatment would be hypo salinty gradually add non salt water to your QT tank lowering the salt level in the tank to about 1.009 to 1.010 but make sure you watch the water closely and watch the fish he should inprove over time(week or two) depending on how sick he is and also if you are feeding him the same food all the time it can cause a blockage in his intestines, try mixing up his diet cause lockjaw can also occur and that i dont know how to fix lol good luck